This invention relates to a method and apparatus for making an electrical coil from conductive wire having an insulating coating bonded thereto and, more particularly, relates to a method and apparatus for providing such a coil with one or more leads that are covered over a portion of their length with electrical insulation. This invention is also concerned with insulated lead structure for such a coil that is so constructed as to readily lend itself to manufacture by a substantially completely automated method.
A typical method that is presently used for making such coils and applying insulated leads thereto is the so-called loop-out method. In this method, a coil winding machine winds the wire into a coil while pulling it past a work station. The winding operation is stopped when a predetermined region of the wire is located at the work station. Then an operator pulls slack into the wire and folds, or loops, this slack out to form in the conductor a loop that will subsequently serve as the desired lead. This loop is then taped in place on the coil, following which a slotted insulating tube is slipped over the loop and is also taped in place. Then the coil winding operation may be resumed.
The above-described looping, taping, and tube-applying steps are manual operations which require considerable time and attention to complete in a satisfactory manner, thus adding substantially to the cost of the resulting coil.
An object of my invention is to construct the insulated lead structure in such a way that it can be produced automatically and without manual intervention and at greatly reduced cost as compared to the cost of the above-described manual procedure.
I am aware of completely automatic methods and apparatus for applying leads to foil, or strip conductor, as the foil is being wound into a coil. See, for example, U.S. Pat. Nos. 3,412,450--Whiteman et al and 3,596,843--Lightner et al. But many of the problems involved in making a coil from wire and particularly from wire having bonded insulation, e.g., enamelled wire, are quite distinct from those involved when the conductor is strip conductor or foil, which typically has a width equal to the axial length of the coil that is being wound. For example, when working with wire having bonded insulation, the tenaciously-adhering bonded insulation usually must first be removed before a separate lead can be attached to the wire. Foil, on the other hand, usually has a bare surface to which the lead can be readily attached. Also, the insulation used for the lead must be quite different in a wire-wound coil, particularly if the lead is a tap located intermediate the ends of the coil. In a wire-wound coil, if the tap is located on an internally-located turn in one layer of coil, the tap must usually extend across and closely adjacent other turns of this layer and must be well insulated from such other turns. But in the foil-wound coil, each layer constitutes a turn, and a tap can extend across the entire width of the layer to which it is attached without necessitating the provision of any insulation between the layer and the tap. This extra insulation required with the taps in a wire-wound coil tends to produce a greater build-up in coil diameter when taps are included in a wire-wound coil than is the case with a foil-wound coil. Moreover, if the tap extends across the entire width of a layer, as in the foil-type coil, the presence of the tap beneath surrounding layers of coil does not cause a non-uniform build-up in the coil diameter across the width of the layers. But in a wire-wound coil, the tap may extend across only a portion of the layer width, thus giving rise to the problem of a non-uniform build-up in core diameter along this layer-width dimension.